Saturday, March 1, 2014

Startup Cuts Lithium-Ion Battery Costs | MIT Technology Review

Bulky and expensive batteries are the bane of electric vehicles. A new MIT spinoff company, SolidEnergy,
says it has a solution: materials that can increase the amount of
energy that lithium-ion batteries store by 30 percent or more and lower
costs enough to make electric vehicles affordable.
The startup recently raised $4.5 million in its first round of
venture funding. It is working with A123 Venture Technologies, part of
the battery maker A123 Systems, to scale up the technology and bring it
to market.
SolidEnergy replaces the graphite electrode used in conventional
lithium-ion batteries with a high-energy lithium-metal one. That’s been
tried before, but the metal tends to cause short circuits and fires. So
the company has also developed improved electrolytes to make them safer.
It plans to sell materials to battery manufacturers, rather than making
batteries itself.
So far, SolidEnergy has made small, hand-built battery cells, similar
to what you would find in a cell phone, using equipment and experts at
an A123 Systems lab near Boston. (A123 Systems went bankrupt last year,
and was acquired by the Chinese company Wanxiang.) These experimental
cells store 30 percent more energy than conventional lithium-ion
batteries, but the company calculates that the approach could eventually
lead to a 40 percent improvement.
The first application of the technology will likely be in portable
electronics, says cofounder and chief technology officer Qichao Hu.
Electric vehicle batteries take longer to develop, in part because they
need to last a decade, whereas batteries for powering electronics need
only last a few years (see “How Tesla Is Driving Electric Car Innovation” and “Will Electric Vehicles Finally Succeed?”).
Lithium-metal electrodes are used in some specialty batteries now,
but the measures that battery makers use to prevent short circuits
weaken the batteries’ performance and increase the cost of making them.
Typically researchers replace the liquid electrolytes used in
conventional lithium-ion batteries with solid polymer ones, which are
poor conductors of lithium ions, and have to be heated up to work
properly.
SolidEnergy uses a two-part electrolyte. First, it coats the lithium
metal with a thin polymer, much like the solid electrolyte others have
used. The key difference is that it’s very thin, so it doesn’t slow down
lithium ions, and the battery doesn’t need to be heated. The thin
polymer can be applied using conventional electrode-coating equipment,
Hu says. On its own, the thin polymer isn’t enough to prevent short
circuits, so he supplements it with a liquid electrolyte.
Unlike conventional liquid electrolytes, the ones SolidEnergy is
using—they’re a type of what’s known as an ionic liquid—are not
flammable, which improves safety. In some recent, highly publicized
battery fires, the part that was burning was primarily the electrolyte